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Nowadays in the aerospace industry the router-based onboard embedded networks gradually replacing bus-based networks because they are already not satisfy the aerospace performance requirements. The SpaceWire, GigaSpaceWire and SpaceFibre standards are developing to meet the increasing aerospace requirements. The important requirement for any aerospace embedded onboard network is a transmission of control information and system signals in hard real time. These signals can be synchronous and asynchronous, periodic and aperiodic, with or without acknowledges. The distributed interrupt mechanism is used for asynchronous signal transmission and it is included into the second edition of SpaceWire standard. The Time-code propagation mechanism is used for synchronous signal transmission in SpaceWire. The broadcast messages mechanism is used for transmission of different system signal in SpaceFibre but it does not quite meet the requirements of hard real time. In this paper the authors consider the asynchronous signals transmission with and without acknowledges. The aims of this paper are following: 1) theoretically investigate the distributed interrupt mechanism; 2) to prove its properties; 3) to specify parameters and limitations; 4) to derive the time characteristics. For these purpose the authors developed the analytical model which describe the distributed interrupt propagation mechanism in terms of the graph theory.

SpaceWire is integrated networking technology where the data packets and control traffic in the form of hard real-time signals are transmitted throw the same links of communication network. Last decades for hard real-time signals transmission in onboard networks the specialized buses like CAN and MIL-STD 155b and sideband signals were used. All buses have the property that the signal from the source node to all other nodes propagates simultaneously, so there is no jitter for signal delivery. When the industry moves to a common communication medium for control and data traffic transmission through network with routing switches and point-to-point connections, there is a problem of synchronization hard real-time signals delivery from the source to all other nodes because of different distance (number of switches and link speeds in a path) between source and receiver. There are many different algorithms and methods for the system time synchronization. In this paper we consider the questions of delivery synchronization of distributed interrupts which intended to control and inform the devices about critical system events in hard real-time.

The distributed interrupt mechanism is intended for reliable and low-latency transmission of system signals with acknowledge in SpaceWire networks. Important tasks are rigorous proof of the distributed interrupt mechanism properties and time characteristics calculation. For these purpose the analytical model has built, which describes the distributed interrupt mechanism in terms of graph theory. The article shows basic data, assumptions and notations for graph theory based model building, describes distributed interrupt propagation algorithm in terms of graph. Here is proved the correctness of the algorithm, i.e.: distributed interrupts/acknowledges wave propagation time is finitely; the distributed interrupts/acknowledges wave propagates to all nodes of a graph. The assertions are proved: acknowledge wave to the interrupt does not cross in time with distributed interrupt wave if the interrupt processing time is greater than the maximum interrupt propagation time; the next interrupt wave does not cross with acknowledge wave to the previous interrupt if the time interval between acknowledge receiving and next interrupt generation is greater than the maximum acknowledge wave propagation time. Here are provides algorithm consequence that Interruptcode (Acknowledge-code) from source node (handler node) to all other graph nodes propagates by the shortest path and forms oriented covering tree. The necessity of the distributed Interrupt mechanism parameters restrictions determined looping problem in networks with loops and provides a solution to this problem, which makes changes to the algorithm and prove the correctness of the changes.